The molecular interactions of oncogenes are complex because they impinge upon elaborate pathways that regulate cellular proliferation and differentiation. In the case of the ski oncogene, this is illustrated by the finding that retroviral mediated overexpression of either v-ski or the proto-oncogene, c-ski, transforms avian embryo fibroblasts and converts them into skeletal myoblasts. V-Ski and c-Ski apparently accomplish these biological feats by binding DNA on their own and in combination with other proteins, and activating transcription via their DNA binding sites. The overall goal of this work is to determine which molecular interactions and activities of ski are responsible for its ability to induce oncogenic transformation. In several of the proposed studies v-ski mutants that are defective in their transforming and myogenic activity will be used to determine which of the biochemical functions of Ski are essential for its biological activity. One of the molecular interactions to be probed is that of Ski and the members of the NF-1 family of transcription/replication factors. Ski activates transcription in combination with some NF-i proteins but not others, and these studies will examine both Ski's role as a co-regulator of NF-i action, and the roles of individual NF-1 forms in the cell-specific action of Ski. Another interaction to be studied is that between ski and the closely related gene, sno. Retroviral overexpression of snoN also leads to transformation of fibroblasts and the present studies will determine whether Ski and Sno function together as transcriptional activators or repressors. Two v-ski mutants which act as dominant negative repressors of both v-ski-induced transformation and c-ski function in normal cellular proliferation and differentiation will serve to probe the role of ski in these processes by examining the nature of the cell cycle block imposed by their action. The ubiquitous expression of c-ski and its pleiotropic effects suggest that Ski must interact with an even more diverse set of partners than those identified above. Additional partners and downstream effectors of Ski function will be sought using DNA binding site selection and differential display of induced and repressed mRNA sequences.